PROJECT SUMMARY This proposal builds on decades of evidence supporting a crucial role for mitochondrial dysfunction and inflammation in neurodegenerative disease. The goal of this proposal is to evaluate the potential of mitochondrial stress signals as predictive biomarkers of Parkinson?s disease (PD) progression. Our working hypothesis is that collective pressure from genetic and environmental risk factors impinges on mitochondrial homeostasis, inducing the release of immunogenic stress signals that drive the aging brain into a pro-inflammatory state. If these stress signals are not resolved, at-risk subjects will have a persistent elevation of oxidative stress that is above the threshold for neurodegeneration, ultimately leading to the clinical manifestation of PD. To date, the earliest and most established mitochondrial stress signal in PD is reactive oxygen species (ROS) production. One of the key signaling functions of mitochondrial ROS is to alert the cellular environment of impending bioenergetic stress. Mitochondrial ROS directly activate microglia, and boost the immunogenicity of other mitochondrial damage associated patterns (mtDAMPs) and ?-synuclein in the at-risk PD brain. The primary ROS produced by stressed mitochondria and activated microglia is superoxide (O2?-). Thus, O2?- provides a signal of mitochondrial and immune (mito-immune) stress. We will determine if this mito-immune signal is a critical driver of PD using the first blood-brain barrier permeant, O2?- - selective PET probe to track PD progression in vivo from the key prodromal features to the end stages in distinct animal models. Our preliminary results support the hypothesis that at-risk PD subjects have increased basal levels of oxidative stress that are 1) detectable by [18F]ROStrace, 2) correlate with PD progression, and 3) sensitize transgenic animals to toxins associated with PD. We now propose to validate these findings in established PD mouse models with prodromal features specifically related to mito-immune stress and ?-synuclein pathology. The progression of the prodromal features will be monitored by changes in dopaminergic signaling via PET/MRI, sleep-wake dynamics, and behavioral tests of mood, olfaction, cognition, and autonomic function, prior to motor impairment caused by loss of dopaminergic neurons. This approach will allow us to investigate the role of mito-immune signaling in conditions mimicking the complexity of PD pathogenesis in the majority of late-onset patients. Our multi-tiered, highly translatable strategy is designed to ensure direct application of this research to the clinic.